1. Field of the Invention
The present invention relates to a synergistic combination composition comprising an ethylene/propylene random copolymer and a low to very low density ethylene/xcex1-olefin random copolymer wherein the xcex1-olefin contains at least 4 carbon atoms. It further relates to polyolefin compositions, in particular polypropylene compositions comprising said synergistic impact modifier combination and a method for improving the impact strength resistance of polyolefin, i.e., the use of said combination as an impact modifier for polyolefins, such as, in particular polypropylene.
2. Description of the Related Art
Crystalline polypropylene is excellent in rigidity, heat resistance, surface gloss, etc., however, the impact resistance of polypropylene is poor and consequently polypropylene is not suitable for many applications.
Various methods have been proposed to improve the impact resistance of polypropylene, for instance, incorporating into crystalline polypropylene modifiers such as polyethylene or rubbery substances, etc. Consequently, a rubbery substance (rubber component), an amorphous or a low crystalline ethylene/propylene random copolymer, polyisobutylene, polybutadiene, etc. are generally used.
In order to improve the impact resistance of polypropylene by incorporation of such a rubbery substance into said polypropylene, however, a large amount of said rubbery substance must be added to the polypropylene. Due to the presence of a large amount of said rubbery substance in the polypropylene composition the impact resistance was in fact improved. However, the rigidity, heat resistance and surface hardness of said compositions was deteriorated. It was proposed in the art to incorporate into said rubbery substance containing polypropylene composition, an inorganic filler such as talc in order to impart rigidity to the compositions.
However, the improvement of the rigidity of a rubbery substance containing polypropylene composition by way of the addition of an inorganic filler is limited.
U.S. Pat. No. 5,591,795 discloses impact modified propylene compositions comprising 60 to 85% by weight of a propylene block copolymer, 10 to 25% by weight of an ethylene/xcex1-olefin random copolymer rubber prepared by using a vanadium-containing catalyst or a metallocene-containing catalyst and 5 to 15% by weight of an inorganic filler, such as talc. The polypropylene is dispersed in the rubber component, which forms the matrix.
It is an object of the present invention to provide an impact modifier which is most suitable for imparting impact resistance to polyolefin compositions, in particular to polypropylene compositions.
Furthermore, it is an object of the present invention to provide a method for imparting impact resistance to polyolefin compositions, in particular to polypropylene compositions, i.e., using the impact modifier according to the present invention to improve the impact strength of polyolefin compositions, in particular of polypropylene compositions.
As a further object of the present invention there should be provided polyolefin compositions, and in detail, polypropylene compositions being improved in their impact strength.
It goes without saying that the overall object is to achieve a superior balance of the important properties of the resulting polyolefin compositions and in detail of the polypropylene compositions by the impact modifier of the present invention. An excellent impact strength should be achieved, while maintaining a superior balance of the overall properties such as melt flow capability, toughness, rigidity and excellent surface aspect.
It has surprisingly been found that the incorporation of a combination of an ethylene/propylene random copolymer (EP) with a low to very low density ethylene/C4 to C20-xcex1-olefin random copolymer shows an synergistic effect in the improvement of the impact resistance of polypropylene compositions while maintaining a good balance of the other important properties, such as melt flow, rigidity, heat resistance and surface aspect.
The combination of the two above-mentioned copolymers can be added to the polyolefin to be modified as a blend or independently.
In detail, in a first aspect the present invention relates to a composition comprising in a blend
(a) 5 to 95% by weight of at least one ethylene/propylene random copolymer, and
(b) 95 to 5% by weight of at least one low to very low density ethylene/C4 to C20-xcex1-olefin random copolymer, based on the total amount of (a) and (b).
Preferably, the ethylene/propylene random copolymer (a) is present in the impact modifier composition (blend) in an amount of 10 to 90% by weight, most preferably 20 to 80% by weight, based on the total amount of (a) and (b).
It is preferred that the impact modifier blend composition according to the present invention contains 90 to 10% by weight, more preferably 80 to 20% by weight, based on the total amount of (a) and (b), of the low to very low density ethylene/xcex1-olefin random copolymer (b).
It is to be noted that the above-mentioned ratio of copolymers (a) and (b) is not only applicable for the blend but also if (a) and (b) are added separately to the polypropylene composition to be modified.
1. Ethylene/propylene Random Copolymer
The ethylene/propylene random copolymer (a) contains up to 80 weight %, preferably from 40 to 65 weight % of ethylene, based on the random copolymer (a).
The ethylene/propylene random copolymer (a) may further contain comonomers selected from non-conjugated dienes such as 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene, 5-methylene-2-norbornene (MNB), 1,6-octadiene, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, 1,3-cyclopentadiene, 1,4-cyclohexadiene, dicyclopentadiene (DCPD) and 5-vinylnorbornene.
Said further comonomers may be present in the ethylene/propylene random copolymer (a) in an amount of up to 15 weight %, preferably in an amount of 0.1 to 5.0 weight %, based on the total amount of the ethylene/propylene random copolymer (a).
Preferably, the ethylene/propylene random copolymer (a) has a density of 0.850 to 0.900 g/cm3 and an intrinsic viscosity [xcex7] in decalin at 135xc2x0 C. of 1 to 6 dl/g.
2. Low to Very Low Density Ethylene/xcex1-olefin Random Copolymer
The ethylene/xcex1-olefin random copolymer (b) present in the impact modifier blend contains the xcex1-olefin in an amount of at least 5 weight %, preferably from 10 to 40 weight %, most preferably from 15 to 30 weight %, based on the total of the random copolymer (b).
The xcex1-olefin to be copolymerized with ethylene is selected from monomers containing at least 4, preferably 4 to 20, more preferably 4 to 12 and most preferably 4 to 8 carbon atoms. Preferred monomers are selected from the group consisting of 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadodecene and mixtures thereof. Out of these comonomers 1-butene, 1-hexene and 1-octene are most preferred. The xcex1-olefins may be present in the random copolymer (b) in a combination of at least two.
The ethylene/xcex1-olefin random copolymer (b) present in the impact modifier composition of the present invention may also contain monomer units derived from monomers other than ethylene and the xcex1-olefin mentioned above. For instance, units derived from dienes containing 5 to 20 carbon atoms, preferably those selected from the non-conjugated dienes mentioned above in context with copolymer (a), may be contained in the random copolymer (b). Preferably their amount is up to 15 weight %, based on the random copolymer (b).
The ethylene/xcex1-olefin random copolymer (b) used in the blend according to the present invention preferably has the following physical properties:
a Mooney viscosity ML (1+4) (ASTM D-1646), as measured at 121xc2x0 C. is from 1 to 50, preferably from 8 to 40,
a density of 0.860 to 0.925 g/cm3, preferably from 0.865 to 0.910 g/cm3 and most preferably from 0.865 to 0.900 g/cm3,
a melt flow index (MFI) according to ASTM D-1238 of from 0.2 to 30 dg/min, preferably from 0.5 to 20 dg/min.
The ethylene/xcex1-olefin random copolymers (b) can be prepared in a known manner by conventional Ziegler-Natta catalysis or metallocene catalysis. Ethylene/xcex1-olefin random copolymers prepared by metallocene catalysis are preferred. These methods are in great detail described in the literature to which it is referred herewith.
According to the invention it has surprisingly been found that the combination comprising (a) and (b) has a synergistic effect on the impact strength of the polypropylene composition to be modified. This means that the combination comprising copolymers (a) and (b) can be used to improve the impact strength resistance particularly of polypropylene compositions, at a level higher than expected from each individual blend ingredient (a) or (b).
Preferably the combination of (a) and (b) is added to the polyolefin to be modified as a melt or tumble blend comprising (a) and (b). The tumble blend can be prepared using any of the conventional tumble blender. The melt-blend of (a) and (b) can conveniently be manufactured in a known manner using conventional mixing devices such as a Banbury-mixer, Farrel continuous mixer (FCM), Henschel-mixer, V-blender, single-screw extruder, multiple-screw extruder or kneader. Mixing/blending of the components (a) and (b) is carried out at a temperature between 150 and 260xc2x0 C., preferably between 150 and 220xc2x0 C.
What is set out above is also applicable if two or more of copolymers (a) and/or two or more of copolymers (b) are employed.
3. Polypropylene
The polypropylene which is impact modified with the impact modifier blend according to the present invention is a conventional polypropylene and is selected from homopolymer, reactor polypropylene copolymer commonly called block-copolymer and random copolymer.
4. Impact Modified Polypropylene
The present invention also relates to a polypropylene composition comprising
(i) a polypropylene
(ii) a combination of at least one ethylene/propylene random copolymer (a) as defined above, and at least one low to very low density, ethylene/xcex1-olefin random copolymer (b) as defined above as the impact modifier, and
(iii) optional additives.
The polypropylene (i) is selected from the type of polypropylene mentioned above and the impact modifier (ii) is selected from the combination as defined above comprising at least one ethylene/propylene random copolymer (a) and at least one of the low to very low density ethylene/xcex1-olefin random copolymer (b).
The optional additives (iii) which may be present in the modified polypropylene composition according to the present invention are selected from the group consisting of inorganic fillers, heat stabilizers, nucleating agents (which include aluminum salts of aromatic carboxylic acid, esters of aromatic phosphoric acid and dibenzylidene sorbitol), ultraviolet absorbers, slip-agents, antistatic agents, flame-retardants, pigments, dyes, inorganic fillers other than finely powdered talc, organic fillers and other polymers, for example, high-density polyethylene, EVA, EMA and EAA.
The inorganic filler mentioned above, which may be present in the impact modified polypropylene compositions according to the present invention, may be selected from finely powdered inorganic materials, for instance talc having an average particle diameter of 0.5 to 20 xcexcm.
The total amount of optional additives may be up to 40% by weight, preferably up to 30% by weight, most preferably between 5 and 20% by weight, based on the total amount of the impact modified polypropylene composition.
The amount of inorganic filler may be up to 40% by weight, preferably up to 30% by weight, most preferably between 5 and 25% by weight, based on the total amount of the impact modified polypropylene composition. The total amount of optional additives including the inorganic filler, however, is not higher than 40% by weight.
The polypropylene composition of the present invention preferably contains from 40 to 96% by weight, preferably from 50 to 90% by weight of polypropylene (i), from 4 to 60% by weight, preferably from 7 to 30% by weight of the inventive impact modifier combination (ii), and from 0 to 40% by weight, preferably from 5 to 25% by weight of the optional additives (iii).
The polypropylene composition of the present invention may be obtained from the components (i), (ii) and optionally (iii) as mentioned above according to conventional known methods for preparing polyolefin compounds (blends), for instance, by feeding the components simultaneously or successively to a mixing device such as a multiple-screw extruder, single-screw extruder, kneader or Banbury mixer or FCM, Henschel mixer or V-blender.
The temperature at which blending is effected is between 150 and 260xc2x0 C., preferably between 150 and 220xc2x0 C.
In this context it should be noted that the impact modifier composition can be added to the polypropylene as a blend or individually, i.e., the at least one ethylene/propylene random copolymer (a) separately from the at least one low to very low density ethylene/xcex1-olefin random copolymer (b).
Injection molded products formed from the polypropylene according to the present invention as described above may be utilized in a wide field of application, such-as for automotive trims, particularly bumpers, instrumental panels, dashboards, etc.